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Biomedical subjects

R M Schaefer

Publications and source records attributed to R M Schaefer.

At least 145 records · Page 8Linked to original sources
PubMed1988

Reduction of muscle protein degradation by leupeptin in acutely uremic rats.

Enhanced muscle protein breakdown has been demonstrated in acutely uremic rats by numerous authors. These findings have been used to explain the clinical signs of muscle wasting and enhanced urea-N appearance, frequently observed in patients suffering from uremia. In order to investigate whether inhibition of skeletal muscle proteinases would have a favourable effect on the extent of muscle protein degradation, leupeptin, a low-molecular-weight proteinase inhibitor, was administered intraperitoneally to acutely uremic rats. 24 h after bilateral nephrectomy, leupeptin-treated animals displayed significantly lowered serum urea levels (-32%), and hence decreased urea-N appearances (-39%) as compared to untreated uremic rats. As a sign of muscle protein breakdown, plasma levels of Nt-methylhistidine, an indicator of myofibrillar protein degradation, were also decreased (-35%) in the uremic animals treated with leupeptin as compared to untreated uremic rats. Finally, leupeptin treatment resulted in a significant inhibition of the myofibrillar alkaline proteinase activity, a proteinase which has been related to various catabolic conditions. These findings suggest that the increased muscle protein breakdown in uremia is caused by enhanced activity of muscular proteinases and that antiproteolytic agents display favourable effects on the enhanced protein degradation observed in acute uremia.

Acute Disease↗
PubMed1988

Change of elastase and cathepsin G content in polymorphonuclear leukocytes during hemodialysis.

Previous studies have demonstrated an increment of polymorphonuclear (PMN) elastase plasma levels during hemodialysis, suggesting release of this proteinase during dialysis treatment. In order to gain further evidence that proteinases are liberated from PMN leukocytes during dialysis both plasma levels of PMN elastase and the content of elastase and cathepsin G in neutrophils were determined during 3 hours of hemodialysis with cellulosic membranes (Cuprophan) in 10 patients. In blood smears, obtained at different times during dialysis, neutrophils were classified into 3 groups according to their proteinase content. Thus, group I neutrophils contained low, group II moderate, and group III leukocytes contained high amounts of both proteinases. With regard to their elastase content, prior to the onset of dialysis, 6% of the circulating PMN leukocytes were classified as fraction I, 58% as fraction II, and 36% as fraction III neutrophils. After 15 minutes of dialysis, at the nadir of leukopenia, all fractions of PMN leukocytes were significantly reduced (fraction I: -9%, fraction II: -60%, and fraction III: -83%) as compared to initial values. 30 minutes into hemodialysis, there was a significant increase in fraction I (+ 78%), whereas fraction II (-28%) and fraction III (-70%) remained diminished. At 180 times of hemodialysis the increment of fraction I neutrophils was even more pronounced (+ 187%), fraction II was also increased (+ 16%), and fraction III neutrophils had almost reached initial values. The cathepsin G content of PMN leukocytes displayed a rather similar pattern during dialysis. As to plasma levels of PMN elastase, there was a steady and significant increase from baseline values of 107.3 +/- 11.5 ng/ml up to 388.1 +/- 51.6 ng/ml after 3 hours of hemodialysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Cathepsin G↗
PubMed1988

Treatment of the anemia of hemodialysis patients with recombinant human erythropoietin.

Fifteen long-term hemodialysis patients suffering from stable anemia received recombinant human erythropoietin (r-huEPO). The hormone was given intravenously at the end of each dialysis session starting with a dose of 24 IU/kg. This dose was doubled when hemoglobin levels did not rise within 2 weeks. The number of reticulocytes started to increase after 14 days of treatment. The hematocrit rose from baseline values of 23.7 +/- 1.2% to 32.4 +/- 1.3% after 24 weeks of treatment. In parallel, hemoglobin values increased from 7.3 +/- 0.3 g/100 ml to 10.1 +/- 0.4 g/100 ml. As for side effects, 3 patients developed hypertension and 2 patients suffered from occlusions of their arterio-venous fistulas. There was no evidence of major organ dysfunctions, toxic effects, allergic reactions, or antibody formation. These data show that r-HuEPO is able to correct the anemia of patients undergoing hemodialysis treatment.

Adult↗
PubMed1987

Effect of dialyzer geometry on granulocyte and complement activation.

During hemodialysis with cuprophan membranes, the complement system as well as leukocytes become activated. In order to clarify the role of dialyzer geometry, the effect of hollow-fiber versus flat-sheet dialyzers and of different surface areas on C3a generation and leukocyte degranulation was investigated. Plasma levels of leukocyte elastase in complex with alpha 1-proteinase inhibitor were significantly increased after 1 h (+55%) and 3 h (+62%) of hemodialysis with flat-sheet dialyzers as compared to hollow-fiber devices. In addition, plasma levels of lactoferrin, released from the specific granules of leukocytes during activation, were significantly higher (+42%) 3 h after the onset of dialysis treatment with flat-sheet than with hollow-fiber dialyzers. With respect to surface area, larger dialyzers tended to cause more release of leukocyte elastase as compared to dialyzers with smaller surface areas, irrespectively of the configuration of the dialyzer used. On the other hand, activation of the complement system, as measured by the generation of C3a-desarg, did not differ with both types of configurations. The same held true for leukopenia, which was almost identical for hollow-fiber and flat-sheet dialyzers. From these findings two lines of evidence emerge: First, not only the type of membrane material used in a dialyzer may influence its biocompatibility, but the geometry of the extracorporeal device also determines the degree of compatibility. Hence, the extent of leukocyte activation correlated with both configuration of the dialyzer and surface area of the membrane.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

Evidence for reduced catabolism by the antiglucocorticoid RU 38486 in acutely uremic rats.

Previous studies suggested that increased blood levels of, or increased tissue sensitivity to, glucocorticoids may contribute to catabolism in acute uremia. To examine this possibility we determined urea nitrogen (urea-N) appearance, plasma levels of Nt-methylhistidine and the activity of the alkaline myofibrillar proteinase in acutely uremic rats with and without treatment with RU 38486, a selective antiglucocorticoid. Forty-eight hours after bilateral nephrectomy, the rats had markedly elevated serum levels of urea-N, creatinine, potassium and phosphorus. In uremic rats receiving RU 38486, comparable levels of serum creatinine were found, but the serum levels of urea-N (221 +/- 4 vs. 259 +/- 5 mg/dl) and phosphorus (6.5 +/- 0.3 vs. 8.5 +/- 0.4 mmol/l) were significantly decreased as compared to uremic animals without RU 38486. In comparison to sham-operated rats, urea-N appearance (net urea production) was increased by 56% 48 h after bilateral nephrectomy. This increment was almost completely reversed in uremic animals receiving the antiglucocorticoid. In untreated uremic rats, plasma levels of Nt-methylhistidine were 10.3 +/- 0.9 microgram/dl, whereas the administration of RU 38486 caused a significant decline in the levels of this amino acid (7.6 +/- 0.5 microgram/dl). This reduction in Nt-methylhistidine was associated with a concomitant decrease of myofibrillar proteinase activity in muscle tissue homogenates. Compared to sham-operated animals, this proteinase activity was increased by 30% in uremic rats, but was normal in those given RU 38486. Taken together, these data support the view that in acute uremia accelerated ureagenesis occurs, while enhanced muscle protein breakdown, owing to an increment in myofibrillar proteinase activity, provides the necessary amino acid precursors.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗
PubMed1987

Enhanced biocompatibility with a new cellulosic membrane: Cuprophan versus Hemophan.

Recently, a new type of modified cellulosic membrane (Hemophan) has been made available for the first clinical trials. In contrast to cellulose acetate membranes only about 5% of the hydroxyl groups of cellulose are substituted by tertiary amino groups. Objective of the present study was to assess the compatibility performance of this new membrane material. Therefore, 10 patients were dialyzed consecutively with membranes made of regenerated cellulose (Cuprophan) and modified cellulose. The modified cellulosic membrane showed less leukopenia. The generation of C3adesarg was reduced throughout the dialysis session. Both, the release of lactoferrin and elastase from granulocytes was diminished with the modified cellulosic membrane. All these differences reached the level of significance. Therefore, it seems that with Hemophan a more biocompatible type of cellulosic membrane has been introduced into hemodialysis treatment.

Biocompatible Materials↗
PubMed1987

Stimulation and inhibition of elastase release from human neutrophil-dependence on the calcium messenger system.

The neutral proteinase elastase is released from polymorphonuclear (PMN) leukocytes in various physiological and pathological conditions. Aim of the present study was to gain further insight into the mechanisms which govern the liberation of this proteinase. Therefore, the effects of the calcium ionophore A23187 and of the protein kinase C activator phorbol myristate acetate (PMA) on neutrophils were investigated in human whole-blood samples. Furthermore, the inhibitory effects of the calcium channel blocker verapamil and of the calmodulin blocker trifluoperazine were followed. A23187 induced a release of elastase from neutrophils in a dose- and time-dependent manner. Complexation of extracellular calcium by ethylenediamine tetraacetate (EDTA) completely abolished the stimulatory effect of A23187. In a concentration of 10(-4) M verapamil was capable of attenuating (-49%) the A23187-induced secretion of PMN elastase. Besides the increase in intracellular calcium concentration, the activation of protein kinase C by PMA did also cause a release of neutrophil elastase. This release was strictly depending on the concentration of PMA and the time of incubation. In contrast to the stimulatory effect of A23187, the PMA-induced liberation of neutrophil elastase was attenuated, but not completely abolished, by complexation of extracellular calcium with EDTA. Both 10(-4) M verapamil (-43%) and 10(-5) M trifluoperazine (-42%) were able to reduce the PMA-induced release of neutrophil elastase. Based upon these data, we conclude that both the translocation of calcium intracellularly by A23187 and the activation of protein kinase C by PMA stimulate the release of neutrophil elastase. Verapamil and trifluoperazine were capable of suppressing the stimulation of elastase release.

Adult↗
PubMed1987

Stimulation and inhibition of elastase release from human neutrophils dependent on the calcium messenger system.

The neutral proteinase elastase is released from polymorphonuclear (PMN) leukocytes in various physiological and pathological conditions. Aim of the present study was to gain further insight into the mechanisms which govern the liberation of this proteinase. Therefore, the effects of the calcium ionophore A23187 and of the protein kinase-C activator phorbol myristate acetate (PMA) on neutrophils were investigated in human whole-blood samples. Furthermore, the inhibitory effects of the calcium channel blocker verapamil and of the calmodulin blocker trifluoperazine were followed. A23187 induced a release of elastase from neutrophils in a dose- and time-dependent manner. Complexation of extracellular calcium by ethylenediamine tetraacetate (EDTA) completely abolished the stimulatory effect of A23187. In a concentration of 10(-4) M verapamil was capable to attenuate (-49%) the A23187-induced secretion of PMN elastase. Beside the increase in intracellular calcium concentration, the activation of protein kinase C by PMA did also cause a release of neutrophil elastase. This release was strictly depending on the concentration of PMA and the time of incubation. In contrast to the stimulatory effect of A23187, the PMA-induced liberation of neutrophil elastase was attenuated, but not completely abolished, by complexation of extracellular calcium with EDTA. Both 10(-4) M verapamil (-43%) and 10(-5) M trifluoperazine (-42%) were able to reduce the PMA-induced release of neutrophil elastase. Based upon these data, we conclude that both the translocation of calcium intracellularly by A23187 and the activation of protein kinase C by PMA stimulate the release of neutrophil elastase. Verapamil and trifluoperazine were capable to suppress the stimulation of elastase release.

Adult↗